Polyene compounds generally are compounds (monomers) having two or more carbon-to-carbon double bonds in one molecule, and many polyene compounds, e.g., 1,3-butadiene, 1,3-pentadiene, 1,4-hexadiene, ethylidene-2-norbornene and dicyclopentadiene, have been hitherto known.
When the polyene compounds are copolymerized with .alpha.-olefins such as ethylene and propylene, vulcanizable unsaturated ethylene copolymers can be obtained. Since the unsaturated ethylene copolymers generally have excellent weathering resistance, heat resistance and ozone resistance, they have been used for rubber products such as automotive industrial parts, industrial rubber products, insulating materials, building and civil engineering materials, and rubberized fabrics. Moreover, they have been widely used as blending materials for plastics such as polypropylene and polystyrene.
Examples of the unsaturated ethylene copolymers conventionally used include an ethylene/propylene/5-ethylidene-2-norbornene copolymer, an ethylene/propylene/dicyclopentadiene copolymer and an ethylene/propylene/1,4-hexadiene copolymer. Of these, the ethylene/propylene/5-ethylidene-2-norbornene copolymer has been particularly widely used, because it has a higher vulcanizing rate as compared with other unsaturated ethylene copolymers.
However, the conventional unsaturated ethylene copolymers are now desired to be further improved in the vulcanizing rate. That is, the unsaturated ethylene copolymers, for example, even the ethylene/propylene/5-ethylidene-2-norbornene copolymer, are low in the vulcanizing rate as compared with diene rubbers such as natural rubbers, styrene/butadiene rubber, isoprene rubber, butadiene rubber and nitrile rubber. Therefore, the co-vulcanizability of the unsaturated ethylene copolymers with the diene rubbers is insufficient.
Further, the vulcanizing rate of the unsaturated ethylene copolymers is lower than that of the diene rubbers, so that it is difficult to prepare vulcanized rubbers therefrom with high productivity by shortening the vulcanizing time, lowering the vulcanizing temperature or reducing the energy consumption in the vulcanization stage.
The vulcanizing rate of the unsaturated ethylene copolymers can be increased by increasing the amount of a vulcanizing agent used. However, if the unsaturated ethylene copolymers are vulcanized using a large amount of a vulcanizing agent, the vulcanizing agent sometimes blooms onto the surface of the resulting vulcanized rubbers, resulting in hygienic disadvantages.
Accordingly, development of a novel polyene compound capable of preparing an unsaturated ethylene copolymer being excellent in weathering resistance, heat resistance and ozone resistance and having a high vulcanizing rate, and development of an unsaturated ethylene copolymer using the polyene compound have been desired.
Under such circumstances mentioned above, the present inventors have earnestly studied polyene compounds and unsaturated ethylene copolymers using the polyene compounds. As a result, they have found that an unsaturated ethylene copolymer using a specific chain polyene group-containing norbornene compound, i.e., an unsaturated ethylene copolymer having constituent units derived from an .alpha.-olefin and a specific chain polyene group-containing norbornene compound and having an unsaturated bond, is excellent in weathering resistance, heat resistance and ozone resistance and has a high vulcanizing rate. Based on this finding, the present invention has been accomplished.
In Japanese Patent Publication No. 42365/1971, there is described a process for preparing an olefin copolymer comprising bringing at least one of ethylene and .alpha.-olefins having the formula RCH.dbd.CH.sub.2 (R: hydrocarbon group having 1 to 20 carbon atoms) and a 5-polyenyl-2-norbornene compound into contact with a coordination catalyst, said 5-polyenyl-2-norbornene compound having the following formula: ##STR2##
wherein R.sup.1 and R.sup.2 are each H or a hydrocarbon group of 1 to carbon atoms, and Q is a hydrocarbon group in which at least one internal double bond is situated at the non-conjugated position and all of the double bonds are of internal type.
However, the olefin copolymer obtained in the process of the above publication is not always sufficient under the circumstances that unsaturated copolymers being excellent in weathering resistance, heat resistance, ozone resistance and vulcanizing rate and having a good balance of these properties are desired.
The present invention is intended to solve such problems associated with the prior art as described above, and it is an object of the invention to provide a chain polyene group-containing norbornene compound suitably used for preparing an unsaturated ethylene copolymer being excellent in weathering resistance, heat resistance and ozone resistance and having a high vulcanizing rate, and to provide a process for preparing the compound.
It is another object of the invention to provide an unsaturated ethylene copolymer of the above properties and a process for preparing the copolymer.
It is a further object of the invention to provide a rubber composition containing the unsaturated ethylene copolymer.